Optical disk manufacturing sheet

ABSTRACT

The present invention provides an optical disk producing sheet  1 , obtained by laminating a stamper-receiving layer  11  that is energy rays-curable and whose storage elastic modulus prior to curing is from 10 3  to 10 7  Pa, and an adhesive layer  12  whose adhesive strength to polycarbonate is at least 200 mN/25 mm, and whose storage elastic modulus during the curing of the stamper-receiving layer  11  is from 10 3  to 10 7  Pa. With the optical disk producing sheet  1 , separation that occurs during the production of an optical disk, or during the storage of the finished product, is prevented, and warpage in the resulting optical disk is reduced.

TECHNICAL FIELD

This invention relates to a sheet used for producing an optical disk,and more particularly relates to an optical disk producing sheet towhich the concavo-convex pattern of a stamper is transferred and pits orgrooves are formed.

BACKGROUND ART

A known method for producing an optical disk is to laminate a dryphoto-setting film (corresponds to the stamper-receiving layer in thepresent invention) on an optical disk substrate composed of apolycarbonate (polycarbonate disk), then press a stamper to the dryphoto-setting film, irradiate the photo-setting film with light to curethe film, then separate the photoset film from the stamper and form alight reflecting layer on the embossed surface of the photoset film(Japanese Patent No. 2,956,989).

Photo-setting films cure when irradiated with light, which decreasestheir adhesive strength and allows them to be separated from a stamper,but at the same time, there is also a decrease in their adhesivestrength to polycarbonate, which is what the optical disk substrate ismade of. Consequently, there is a problem that separation will occurbetween a photoset film and an optical disk substrate made ofpolycarbonate during the production of the optical disk, or thatinterlayer separation will occur under certain conditions during thestorage of the completed optical disk.

Also, the curing reaction induced by irradiation with light causes aphoto-setting film to shrink, and the shrinkage stress produced in thephoto-setting film by the shrinkage exerts a force in the shrinkagedirection against the side of the optical disk substrate that is incontact with the photo-setting film, resulting in warping in the opticaldisk that is obtained.

DISCLOSURE OF THE INVENTION

The present invention was conceived in light of this situation, and itis an object thereof to provide an optical disk producing sheet, withwhich separation that occurs during the production of an optical disk,or during the storage of the finished product, is prevented, and warpagein the resulting optical disk is reduced.

To achieve the stated object, the present invention provides an opticaldisk producing sheet, comprising a stamper-receiving layer that isenergy rays-curable and whose storage elastic modulus prior to curing isfrom 10³ to 10⁷ Pa, and an adhesive layer whose adhesive strength topolycarbonate is at least 200 mN/25 mm, and whose storage elasticmodulus during the curing of the stamper-receiving layer is from 10³ to10⁷ Pa, wherein the stamper-receiving layer and the adhesive layer arelaminated (1).

With the above invention (1), the adhesive strength of the adhesivelayer with respect to polycarbonate is set higher than the ordinaryadhesive strength of the cured stamper-receiving layer with respect tothe stamper, so when the cured stamper-receiving layer and the stamperare separated each other, there is no separation between the adhesivelayer (stamper-receiving layer) and the polycarbonate substrate, sheet,film, or other such polycarbonate layer.

Also, with the above invention (1), the stamper-receiving layer can bebonded to a polycarbonate layer via the adhesive layer that has highadhesive strength to polycarbonate, which prevents separation betweenthe polycarbonate layer and the stamper-receiving layer during storageof the finished product.

Furthermore, with the above invention (1), because the storage elasticmodulus of the adhesive layer is from 10³ to 10⁷ Pa during the curing ofthe stamper-receiving layer, even if the curing reaction producesshrinkage stress in the stamper-receiving layer, the adhesive layer isable to moderate the shrinkage stress and reduce the force in theshrinkage direction exerted by the stamper-receiving layer on theoptical disk substrate, cover sheet, or other such component to bebonded, which makes it possible to reduce warpage of the resultingoptical disk.

With the above invention (1), the adhesive layer is preferablyconstituted by a pressure sensitive adhesive (2), and in the aboveinvention (2), the pressure sensitive adhesive preferably has as aconstituent component an acrylic ester copolymer (3). An adhesive suchas this has excellent adhesion to the stamper-receiving layer and topolycarbonate, and its storage elastic modulus can be easily set to therange given above.

With the above inventions (1 to 3), the stamper-receiving layerpreferably has as a constituent component an acrylic ester copolymerhaving an energy rays-curable group on a side chain thereof (4). Thisacrylic ester copolymer has properties that are favorable as thestamper-receiving layer, making possible the precise transfer to theconcavo-convex pattern on the stamper, and when it is separated from thestamper after curing, there is almost no deposition onto the stamper.

With the above inventions (1 to 4), the stamper-receiving layerpreferably contains a carboxyl group-containing copolymer obtained bycopolymerizing at least one type of monomer having a carboxyl group (5).When carboxyl groups are present in the material constituting thestamper-receiving layer, the adhesive strength between thestamper-receiving layer and a reflecting film composed of a metal thinlayer formed on the stamper-receiving layer will be higher, whichprevents separation between the stamper-receiving layer and thereflecting film during the storage of the finished product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of the optical disk producing sheet pertainingto an embodiment of the present invention;

FIG. 2 is a cross section of an example of an optical disk producingmethod in which the optical disk producing sheet pertaining to the sameembodiment is used; and

FIG. 3 is a cross section of another example of an optical diskproducing method in which the optical disk producing sheet pertaining tothe same embodiment is used.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described.

[Optical Disk Manufacturing Sheet]

FIG. 1 is a cross section of the optical disk producing sheet pertainingto an embodiment of the present invention.

As shown in FIG. 1, the optical disk producing sheet 1 pertaining tothis embodiment is obtained by laminating a release sheet 13′, anadhesive layer 12, a stamper-receiving layer 11, and a release sheet 13.The release sheets 13 and 13′ are peeled off when the optical diskproducing sheet 1 is used.

The stamper-receiving layer 11 is a layer on which concavo-convexpattern formed on the stamper is transferred and pits or grooves areformed. This stamper-receiving layer 11 is energy rays-curable, and thestorage elastic modulus of the stamper-receiving layer 11 prior tocuring is from 10³ to 10⁷ Pa, and preferably from 10⁴ to 5×10⁶ Pa.

Here, the temperature at which the “storage elastic modulus prior tocuring” is measured is to be the same as the temperature of the workingenvironment in which the stamper and the optical disk producing sheet 1are superimposed (pressed together). Specifically, when the stamper andthe optical disk producing sheet 1 are superimposed at room temperature,the storage elastic modulus is measured at room temperature, and whenthe stamper and the optical disk producing sheet 1 are superimposedunder heating, the storage elastic modulus is measured at the sametemperature as the heating temperature.

If the storage elastic modulus of the stamper-receiving layer 11 priorto curing is within the above range, merely pressing the stamper to thestamper-receiving layer 11 can precisely transfer the concavo-convexpattern formed on the stamper onto the stamper-receiving layer 11,making it extremely easy to produce an optical disk.

The storage elastic modulus of the stamper-receiving layer 11 aftercuring is preferably at least 10⁷ Pa, with 10⁸ to 10¹¹ Pa beingparticularly favorable. Here, the temperature at which the “storageelastic modulus after curing” is measured is to be the same as thetemperature of the environment in which the optical disk is stored, thatis, room temperature.

If the storage elastic modulus of the stamper-receiving layer 11 aftercuring is within the above range, the pits or grooves transferred to thestamper-receiving layer 11 can be securely fixed by curing, so therewill be no danger of the pits or grooves being destroyed or deformed inthe course of separating the stamper and the stamper-receiving layer 11.

The main component of the stamper-receiving layer 11 is preferably anenergy rays-curable polymer, but the main component may also be amixture of a polymer that is not energy rays-curable and an energyrays-curable polyfunctional monomer or oligomer.

The stamper-receiving layer 11 will now be described for a case in whichthe main component is an energy rays-curable polymer.

The energy rays-curable polymer component that constitutes thestamper-receiving layer 11 is preferably an acrylic ester copolymerhaving an energy rays-curable group on a side chain thereof. Thisacrylic ester copolymer is preferably an energy rays-curable copolymer(A) having a molecular weight of at least 100,000 and having an energyrays-curable group on a side chain thereof, obtained by reacting anacrylic copolymer (a1) having monomer units that contain functionalgroups and a unsaturated group-containing compound (a2) havingsubstituents that bond to these functional groups.

The acrylic copolymer (a1) is composed of structural units derived froma monomer containing a functional group, and structural units derivedfrom a (meth)acrylic ester monomer or derivative thereof.

The monomer containing a functional group in the acrylic copolymer (a1)is a monomer having in its molecule a polymerizable double bond and afunctional group such as a hydroxyl group, carboxyl group, amino group,substituted amino group, or epoxy group, and is preferably anunsaturated monomer containing a hydroxyl group or an unsaturatedmonomer containing a carboxyl group.

More specific examples of such monomers containing a functional groupinclude 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, and other suchacrylates containing a hydroxyl group, and acrylic acid, methacrylicacid, itaconic acid, and other such compounds containing a carboxylgroup. These can be used singly or in combinations of two or more.

This monomer containing a functional group is preferably selected suchthat carboxyl groups can be present in the energy rays-curablecopolymer. If carboxyl groups are present in the energy rays-curablecopolymer, the adhesive strength between stamper-receiving layer 11 andthe metal thin layer (such as a reflective layer used for recording andplayback) formed on the stamper-receiving layer 11 can be higher, whichimproves the strength and durability of the resulting optical disk.

The amount of the carboxyl groups which are present in the energyrays-curable copolymer, in terms of monomer, is preferably from 0.01 to30 mol %, and even more preferably from 5.0 to 20 mol %. When carboxylgroups are reacted with the unsaturated group-containing compound (a2)discussed below (that is, when the functional group-containing monomeris a carboxyl group-containing monomer), the carboxyl group content isthe value calculated on the basis of(number of moles of carboxyl group-containing monomer)−(number of molesof unsaturated group-containing compound).

A cycloalkyl (meth)acrylate, a benzyl (meth)acrylate, or a (meth)acrylicalkyl ester in which the carbon number of the alkyl group is from 1 to18 is used as the (meth)acrylic ester monomer that constitutes theacrylic copolymer (a1). Of these, it is particularly favorable to use a(meth)acrylic alkyl ester in which the carbon number of the alkyl groupis from 1 to 18, such as methyl (meth)acrylate, ethyl (meth)acrylate,propyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl(meth)acrylate or the like.

The acrylic copolymer (a1) contains structural units derived from theabove-mentioned functional group-containing monomer in a ratio that isusually 3 to 100 wt %, and preferably 5 to 40 wt %, and especially 10 to30 wt %, and contains structural units derived from a (meth)acrylicester monomer or derivative thereof in a ratio that is usually 0 to 97wt %, and preferably 60 to 95 wt %, and especially 70 to 90 wt %.

The acrylic copolymer (a1) is obtained by copolymerizing theabove-mentioned functional group-containing monomer and the(meth)acrylic ester monomer or derivative thereof by a standard method,but a small amount (such as a proportion of 10 wt % or less, andpreferably 5 wt % or less) of vinyl formate, vinyl acetate, styrene, orthe like may also be copolymerized in addition to the above monomers.

The energy rays-curable copolymer (A) is obtained by reacting theabove-mentioned acrylic copolymer (a1) having functionalgroup-containing monomer units with an unsaturated group-containingcompound (a2) having a substituent that bonds to the functional group.

The substituent in the unsaturated group-containing compound (a2) can besuitably selected according to the type of functional group of thefunctional group-containing monomer in the acrylic copolymer (a1). Forinstance, when the functional group is a hydroxyl group, amino group, orsubstituted amino group, an isocyanate group or epoxy group is favorableas the substituent; when the functional group is a carboxyl group, anaziridinyl group, epoxy group, or oxazoline group is favorable as thesubstituent; and when the functional group is an epoxy group, an aminogroup, carboxyl group, or aziridinyl group is favorable as thesubstituent. One such substituent is contained per molecule of theunsaturated group-containing compound (a2).

The unsaturated group-containing compound (a2) has 1 to 5, andpreferably 1 to 2, energy rays-curable carbon-carbon double bonds permolecule. Specific examples of such an unsaturated group-containingcompound (a2) include methacryloyloxyethyl isocyanate,meta-isopropenyl-α,α-dimethylbenzyl isocyanate, methacryloyl isocyanate,allyl isocyanate; an acryloyl monoisocyanate compound obtained byreacting a diisocyanate compound or polyisocyanate compound and ahydroxyethyl (meth)acrylate; an acryloyl monoisocyanate compoundobtained by reacting a diisocyanate compound or polyisocyanate compound,a polyol compound, and a hydroxyethyl (meth)acrylate; glycidyl(meth)acrylate; (meth)acrylic acid, 2-(1-aziridinyl)ethyl(meth)acrylate,2-vinyl-2-oxazoline, and 2-isopropenyl-2-oxazoline.

The unsaturated group-containing compound (a2) is usually used in aproportion of 20 to 100 equivalents, and preferably 40 to 95equivalents, and especially 60 to 90 equivalents, per 100 equivalents ofthe functional group-containing monomer of the acrylic copolymer (a1).

In the reaction between the acrylic copolymer (a1) and the unsaturatedgroup-containing compound (a2), the temperature, pressure, solvent,duration, use of a catalyst, and type of catalyst can be suitablyselected according to the combination of the functional group and thesubstituent. As a result, the functional groups present in side chainsof the acrylic copolymer (a1) react with the substituents in theunsaturated group-containing compound (a2), unsaturated groups areintroduced into the side chains of the acrylic copolymer (a1), and theenergy rays-curable copolymer (A) is obtained. The reaction rate of thefunctional groups and substituents in the reaction is usually at least70%, and preferably at least 80%, and unreacted functional groups canremain in the energy rays-curable copolymer (A).

The weight average molecular weight of the energy rays-curable copolymer(A) obtained in this manner is at least 100,000, and preferably from150,000 to 1,500,000, and especially from 200,000 to 1,000,000.

Here, when ultraviolet rays are used as the energy rays, thepolymerization curing time and the irradiation dose can be reduced byadding a photopolymerization initiator (B) to the energy rays-curablecopolymer (A).

Specific examples of the photopolymerization initiator (B) includebenzophenone, acetophenone, benzoin, benzoin methyl ether, benzoin ethylether, benzoin isopropyl ether, benzoin isobutyl ether, benzoin benzoicacid, methyl benzoin benzoate, benzoin dimethyl ketal,2,4-diethylthioxanthone, 1-hydroxycyclohexyl phenyl ketone, benzyldiphenyl sulfide, tetramethylthiuram monosulfide,azobisisobutyronitrile, benzyl, dibenzyl, diacetyl,β-chloranthraquinone, (2,4,6-trimethylbenzyldiphenyl)phosphone oxide,2-benzothiazole-N,N-diethyldithiocarbamate, andoligo{2-hydroxy-2-methyl-1-[4-(1-propenyl)phenyl]propanone}. These maybe used singly or in combinations of two or more. Thephotopolymerization initiator (B) is used in an amount of 0.1 to 10parts by weight of, and particularly 0.5 to 5 parts by weight of, per100 parts by weight of the energy rays-curable copolymer (A).

Other components may be added as needed along with the energyrays-curable copolymer (A) and the photopolymerization initiator (B) inthe stamper-receiving layer 11. Examples of other components include apolymer component or oligomer component that is not energy rays-curable(C), a polyfunctional monomer or oligomer component that is energyrays-curable (D), a crosslinking agent (E), and other additives (F).

Examples of the polymer component or oligomer component that is notenergy rays-curable (C) include polyacrylic ester, polyester,polyurethane, polycarbonate, and polyolefin. A polymer or oligomer witha weight average molecular weight of 3,000 to 2,500,000 is preferred.

Examples of the polyfunctional monomer or oligomer component that isenergy rays-curable (D) include trimethylolpropane tri(meth)acrylate,pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol hexa(meth)acrylate, 1,4-butanediol di(meth)acrylate,1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate,polyester oligo(meth)acrylate, and polyurethane oligo(meth)acrylate.

As the crosslinking agent (E), a polyfunctional compound that isreactive with the functional groups in the energy rays-curable copolymer(A) and so forth can be used. Examples of such polyfunctional compoundsinclude isocyanate compounds, epoxy compounds, amine compounds, melaminecompounds, aziridine compounds, hydrazine compounds, aldehyde compounds,oxazoline compounds, metal alkoxide compounds, metal chelate compounds,metal salts, ammonium salts, and reactive phenol resins.

Examples of the other additives (F) include UV absorbents, plasticizers,fillers, antioxidants, tackifiers, pigments, dyes, and coupling agents.

The addition of these other components (C) to (F) to thestamper-receiving layer 11 sometimes improves ease of transfer of theconcavo-convex pattern prior to curing, strength after curing, adhesionto and release from other layers, and storage stability.

A case will now be described in which the main component of thestamper-receiving layer 11 is a mixture of a polymer component that isnot energy rays-curable and a polyfunctional monomer or oligomer that isenergy rays-curable.

The same components as with the acrylic copolymer (a1) discussed abovecan be used as the polymer component used in the stamper-receiving layer11. Of the acrylic copolymers (a1), it is preferable to select anacrylic copolymer that has carboxyl groups as functional groups becausethis will afford better adhesion between the stamper-receiving layer 11and the metal thin layer formed on the stamper-receiving layer 11.

The polyfunctional monomer or oligomer that is energy rays-curable canbe selected the same as with component (D) discussed above. The blendratio of the polymer component and the polyfunctional monomer oroligomer that is energy rays-curable is preferably 10 to 150 parts byweight of, and especially 25 to 100 parts by weight of polyfunctionalmonomer or oligomer per 100 parts by weight of polymer component.

The other additives (F) discussed above can also be added to thestamper-receiving layer 11. Even when these other additives (F) areadded, though, the storage elastic modulus of the stamper-receivinglayer 11 still needs to be between 10³ and 10⁷ Pa, and it is preferablefor the design to reduce the amount of deposits remaining from thestamper-receiving layer 11 on the stamper. The amount in which theseother additives (F) are added is preferably 0 to 50 parts by weight of,and especially 0 to 20 parts by weight of the total amount of theseother additives (F) per 100 parts by weight of the energy rays-curablecopolymer (A).

Here, the thickness of the stamper-receiving layer 11 is determinedaccording to the depth of the pits or grooves to be formed, but isusually about 5 to 30 μm, and preferably about 10 to 20 μm.

Meanwhile, the adhesive layer 12 serves to bond the stamper-receivinglayer 11 to an optical disk substrate or cover sheet. The optical disksubstrate or cover sheet is substantially made of polycarbonate in orderto satisfy the optical characteristics required of an optical disk.

The adhesive strength of the adhesive layer 12 to polycarbonate is atleast 200 mN/25 mm, and preferably at least 400 mN/25 mm. Such adhesivestrength of the adhesive layer 12 can prevent the optical disk producingsheet from separating from the polycarbonate material. Also, even in theevent that the optical disk is stored over the long term, interfacialseparation at the adhesive layer 12 that would otherwise result frominadequate adhesive strength of the adhesive layer 12 can be prevented.

The storage elastic modulus of the adhesive layer 12 is from 10³ to 10⁷Pa, and preferably 10⁴ to 10⁶ Pa, during the curing of thestamper-receiving layer 11. The stamper-receiving layer 11 will shrinkas the curing reaction proceeds (approximately 3 to 7% as volumetricshrinkage), but as long as the storage elastic modulus of the adhesivelayer 12 is within the above range, even if shrinkage stress is producedin the stamper-receiving layer 11, the adhesive layer 12 will be able tomoderate the shrinkage stress and reduce the force in the shrinkagedirection exerted by the stamper-receiving layer on the object beingbonded (optical disk substrate or cover sheet), which makes it possibleto reduce warpage of the resulting optical disk. If the storage elasticmodulus of the adhesive layer 12 is less than 10³ Pa, the adhesive layer12 may be deformed by the heat produced in the formation of a reflectivelayer by sputtering or the like on the stamper-receiving layer 11, orthe adhesive layer 12 may be deformed over time even at normaltemperature.

The adhesive layer 12 is preferably constituted by a pressure sensitiveadhesive, which may be either a non-curable pressure sensitive adhesiveor a curable pressure sensitive adhesive. As to the type of pressuresensitive adhesive, it may be based on acrylic, polyester, urethane,rubber, silicone, or the like, but of these, it is preferable to use anacrylic pressure sensitive adhesive in which an acrylic ester copolymeris a constituent component.

Examples of favorable acrylic ester copolymers include a copolymerobtained by copolymerizing (meth)acrylic esters in which the alkyl groupof the ester portion has a carbon number of 1 to 20, a monomer having afunctional group that contains active hydrogen, and another monomerwhich can be used as desired.

Examples of (meth)acrylic esters in which the alkyl group of the esterportion has a carbon number of 1 to 20 include methyl (meth)acrylate,ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate,pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate,2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, decyl(meth)acrylate, dodecyl (meth)acrylate, myristyl (meth)acrylate,palmityl (meth)acrylate, and stearyl (meth)acrylate. These may be usedsingly or in combinations of two or more.

Examples of monomers having a functional group that contains activehydrogen include 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl(meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl(meth)acrylate, and other such hydroxyalkyl esters of (meth)acrylicacid; acrylamide, methacrylamide, N-methylacrylamide,N-methylmethacrylamide, N-methylolacrylamide, N-methylolmethacrylamide,and other such acrylamides; monomethylaminoethyl (meth)acrylate,monoethylaminoethyl (meth)acrylate, monomethylaminopropyl(meth)acrylate, monoethylaminopropyl (meth)acrylate, and other suchmonoalkylaminoalkyl (meth)acrylates; and acrylic acid, methacrylic acid,crotonic acid, maleic acid, itaconic acid, citraconic acid, and othersuch ethylenic unsaturated carboxylic acids. These monomers may be usedsingly or in combinations of two or more.

Examples of other monomers used as desired include vinyl acetate, vinylpropionate, and other such vinyl esters; styrene, α-methylstyrene, andother such styrene monomers; butadiene, isoprene, chloroprene, and othersuch diene monomers; acrylonitrile, methacrylonitrile, and other suchnitrile monomers; and N,N-dimethylacrylamide,N,N-dimethylmethacrylamide, and other such N,N-dialkyl-substitutedacrylamides. These monomers may be used singly or in combinations of twoor more.

There are no particular restrictions on the copolymerizationconfiguration of the acrylic ester copolymer, which may be either arandom copolymer, a block copolymer, or a graft copolymer. In order toensure good reliability of the optical disk, the weight averagemolecular weight of the acrylic ester copolymer is preferably between500,000 and 2,000,000. This weight average molecular weight is the valuecalculated as polystyrene, measured by gel permeation chromatography(GPC).

The above acrylic ester copolymers may be used singly or in combinationsof two or more.

The above-mentioned acrylic pressure sensitive adhesive preferablycontains a crosslinking agent. There are no particular restrictions onthe type of crosslinking agent, which can be any crosslinking agent usedin conventional acrylic pressure sensitive adhesive. For example, onecan be suitably selected from among polyisocyanate compounds, epoxyresins, melamine resins, urea resins, dialdehydes, methylol polymers,metal chelate compounds, metal alkoxides, metal salts, and so on.

The adhesive layer 12 may contain various components as desired, butpreferably has a low content of components that would corrodepolycarbonate, such as acrylamide and other such basic components.

The adhesive layer 12 may be constituted by an adhesive that is curable,such as one that is energy rays-curable, in which case the storageelastic modulus of the adhesive layer 12 should be from 10³ to 10⁷ Paduring the curing of the stamper-receiving layer 11.

The constituent material of the energy rays-curable adhesive can be thesame component as the energy rays-curable polymer component thatconstituents the stamper-receiving layer 11 as described above. In orderto keep the storage elastic modulus of the adhesive layer 12 within theabove range, however, the unsaturated group-containing compound (a2) ispreferably used in a proportion of 1 to 20 equivalents per 100equivalents of the functional group-containing monomer of the acryliccopolymer (a1), and the blend ratio of the polymer and thepolyfunctional monomer or oligomer that is energy rays-curable ispreferably 1 to 20 parts by weight of polyfunctional monomer or oligomerper 100 parts by weight of polymer component.

The thickness of the adhesive layer 12 is usually about 5 to 30 μm, andpreferably about 10 to 20 μm.

With the optical disk producing sheet 1 pertaining to this embodiment,the stamper-receiving layer 11 and the adhesive layer 12 are prone todeformation under pressure, and in order to prevent this, the releasesheet 13 is laminated to the stamper-receiving layer 11, and the releasesheet 13′ is laminated to the adhesive layer 12. The release sheets 13and 13′ can be types known in the past; for example, a polyethyleneterephthalate, polypropylene, or other resin film that has undergone arelease treatment with a silicone release agent or the like can be used.

In order to impart smoothness to the stamper-receiving layer 11, therelease sheet 13 preferably has a surface roughness (Ra) of no more than0.1 μm on the side that has undergone the release treatment (the side incontact with the stamper-receiving layer 11). The thickness of therelease sheets 13 and 13′ is usually about 10 to 200 μm, and preferablyabout 20 to 100 μm.

Usually, the release sheet 13′ is peeled away first, and the releasesheet 13 is peeled away later, so it is preferable for the release sheet13′ to be a light-release type, and for the release sheet 13 to be aheavy-release type, but whether the release sheet 13 on thestamper-receiving layer 11 side is peeled first, or the release sheet13′ on the adhesive layer 12 side is peeled first can vary with theoptical disk producing procedure, so whether a light-release type orheavy-release type is used for the release sheets 13 and 13′ laminatedon either side can be determined by the selected optical disk producingprocedure.

[Production of Optical Disk Producing Sheet]

To produce the optical disk producing sheet 1 pertaining to thisembodiment, first a coating agent for the stamper-receiving layer 11containing the material that constituted the stamper-receiving layer 11and, if desired, a solvent is prepared, and a coating agent for theadhesive layer 12 containing the material that constituted the adhesivelayer 12 and, if desired, a solvent is prepared.

Then, (1) the stamper-receiving layer 11 is formed by applying thecoating agent for the stamper-receiving layer 11 to the release sheet13, after that the adhesive layer 12 is formed by applying the coatingagent for the adhesive layer 12 to the stamper-receiving layer 11, andthe other release sheet 13′ is laminated on the surface of the adhesivelayer 12, (2) the adhesive layer 12 is formed by applying the coatingagent for the adhesive layer 12 to the release sheet 13′, after that thestamper-receiving layer 11 is formed by applying the coating agent forthe stamper-receiving layer 11 to the adhesive layer 12, and the otherrelease sheet 13 is laminated on the surface of the stamper-receivinglayer 11, (3) the stamper-receiving layer 11 is formed by applying thecoating agent for the stamper-receiving layer 11 to the release sheet13, while the adhesive layer 12 is formed by applying the coating agentfor the adhesive layer 12 to the release sheet 13′, and thestamper-receiving layer 11 and the adhesive layer 12 are laminated bybeing superposed one over the other, or (4) the coating agent for thestamper-receiving layer 11 and the coating agent for the adhesive layer12 are simultaneously applied by co-extrusion to form thestamper-receiving layer 11 and the adhesive layer 12. The coating agentscan be applied, for example, with a kiss roll coater, a reverse rollcoater, a knife coater, a roll knife coater, a die coater, or anothersuch coating machine.

[Production of Optical Disk (1)]

An example will be described of the method for producing an optical diskusing the above-mentioned optical disk producing sheet 1. FIGS. 2( a) to2(h) are cross sections illustrating an example of producing an opticaldisk using the optical disk producing sheet 1.

First, as shown in FIGS. 2( a) and 2(b), the release sheet 13 is peeledaway from the stamper-receiving layer 11 side of the optical diskproducing sheet 1, and the exposed stamper-receiving layer 11 is pressedto a stamper S to transfer the concavo-convex pattern of the stamper Sonto the stamper-receiving layer 11. If the storage elastic modulus ofthe stamper-receiving layer 11 at room temperature is between 10³ and10⁷ Pa, the pressing of the stamper S can be performed at roomtemperature.

The stamper S is made from a metal material such as a nickel alloy, or atransparent resin material such as a norbornene resin. The stamper Sshown in FIGS. 2( a) to 2(e) is in the form of a sheet, but is notlimited to this, and may instead be in the form of a roll.

Next, as shown in FIG. 2( c), the release sheet 13′ is peeled off theadhesive layer 12, and a cover sheet 6 composed of polycarbonate islaminated and press bonded to the exposed adhesive layer 12. This coversheet 6 constitutes the light receiving side of the optical disk.

Then, as shown in FIG. 2( d), with the stamper S held tightly againstthe stamper-receiving layer 11, an energy ray irradiation apparatus (aUV lamp L is shown as an example in FIG. 2( d)) is used to irradiate thestamper-receiving layer 11 with energy rays from the cover sheet 6 side.The energy rays-curable material that constitutes the stamper-receivinglayer 11 is cured thereby, and the storage elastic modulus is increased.

Ultraviolet rays, electron rays, or the like is usually used as theenergy rays. The irradiation dose of energy rays can vary with the typeof energy rays being used, but in the case of ultraviolet rays, forinstance, about 100 to 500 mJ/cm² of light quantity is preferable, whilein the case of electron rays, about 10 to 1000 krad is preferable.

At this time, the curing of the energy rays-curable material producesshrinkage stress in the stamper-receiving layer 11, but the adhesivelayer 12 is able to moderate the shrinkage stress and reduce the forcein the shrinkage direction exerted by the stamper-receiving layer 11 tothe cover sheet 6, which reduces warpage of the cover sheet 6 and, also,the resulting optical disk.

After that, as shown in FIG. 2( e), the stamper S is separated from thestamper-receiving layer 11. Since the adhesive strength of the adhesivelayer 12 to polycarbonate is at least 200 mN/25 mm, and is set higherthan the adhesive strength of the stamper-receiving layer 11 to thestamper S, the separation of the adhesive layer 12 and the cover sheet 6is prevented when the stamper S is separated from the stamper-receivinglayer 11.

Once the concavo-convex pattern of the stamper S has been transferred toand fixed on the stamper-receiving layer 11 to form pits or grooves asabove, a translucent reflective layer 4′ composed of silver, a silveralloy, aluminum, or another such metal thin layer is then formed on thesurface of the stamper-receiving layer 11 by sputtering or another suchmeans as shown in FIG. 2( f).

Here, if carboxyl groups are present in the material that constitutesthe stamper-receiving layer 11 here, the adhesive strength between thestamper-receiving layer 11 and the translucent reflective layer 4′ canbe higher, which increases the strength, durability, and so forth of theoptical disk that is obtained.

Apart from the cover sheet 6, adhesive layer 12, stamper-receiving layer11, and translucent reflective layer 4′, as shown in FIG. 2( g), anoptical disk substrate 3 that is composed of polycarbonate and has aspecific concavo-convex pattern is formed by injection molding oranother such molding method, and a reflective layer 4 composed of ametal thin layer is formed by sputtering or another such means over theconcavo-convex pattern.

Finally, as shown in FIG. 2( h), the laminate on which the translucentreflective layer 4′ is formed (the cover sheet 6+the adhesive layer12+the stamper-receiving layer 11+the translucent reflective layer 4′)and the optical disk substrate 3 on which the reflective layer 4 isformed are bonded via an adhesive 5 so that the translucent reflectivelayer 4′ and the reflective layer 4 face each other.

The result of the above is that interlayer separation is prevented, andan optical disk with almost no warpage (less than 0.2° warpage) isobtained.

[Production of Optical Disk (2)]

Another example will be described of the method for producing an opticaldisk using the above-mentioned optical disk producing sheet 1. FIGS. 3(a) to 3(g) are cross sections illustrating an example of producing anoptical disk using the optical disk producing sheet 1.

First, as shown in FIG. 3( a), an optical disk substrate 3 having aspecific concavo-convex pattern is formed by injection molding oranother such molding method, and a reflective layer 4 composed of ametal thin layer is formed by sputtering or another such means over theconcavo-convex pattern. Here, the reflective layer 4 is not to formed atthe edge portion of the optical disk substrate 3, so polycarbonate,which is the material of the optical disk substrate 3, is exposed aroundthe edge portion of the optical disk substrate 3.

As shown in FIG. 3( b), the release sheet 13′ on the adhesive layer 12of the optical disk producing sheet 1 is peeled away, and the exposedadhesive layer 12 is laminated and press bonded to the optical disksubstrate 3 on which the reflective layer 4 has been formed. Then, asshown in FIG. 3( c), the release sheet 13 laminated over thestamper-receiving layer 11 is peeled away to expose thestamper-receiving layer 11.

Next, as shown in FIG. 3( d), a transparent stamper S is pressed to theexposed stamper-receiving layer 11, and the concavo-convex pattern ofthe stamper S is transferred to the stamper-receiving layer 11. In thisstate, an energy ray irradiation apparatus (a UV lamp L is shown as anexample in FIG. 3( d)) is used to irradiate the stamper-receiving layer11 with energy rays from the stamper S side. This cures thestamper-receiving layer 11.

At this time, the curing of the energy rays-curable material producesshrinkage stress in the stamper-receiving layer 11, but the adhesivelayer 12 is able to moderate the shrinkage stress and reduce the forcein the shrinkage direction exerted by the stamper-receiving layer 11 tothe optical disk substrate 3, which reduces warpage of the 3 and, also,the resulting optical disk.

After that, as shown in FIG. 3( e), the stamper S is separated from thestamper-receiving layer 11. Since the adhesive strength of the adhesivelayer 12 to polycarbonate is at least 200 mN/25 mm, and the adhesivelayer 12 is bonded at high adhesive strength to the polycarbonateportion around the edges of the optical disk substrate 3, the separationof the adhesive layer 12 and the optical disk substrate 3 is preventedwhen the stamper S is separated from the stamper-receiving layer 11.

Once the concavo-convex pattern of the stamper S has been transferred toand fixed on the stamper-receiving layer 11 to form pits or grooves asabove, a translucent reflective layer 4′ composed of a metal thin layeris then formed on the surface of the stamper-receiving layer 11 bysputtering or another such means as shown in FIG. 3( f).

Finally, as shown in FIG. 3( g), the cover sheet 6 is laminated to thetranslucent reflective layer 4′ via the adhesive 5 to obtain an opticaldisk.

The result of the above is that interlayer separation is prevented, andan optical disk with almost no warpage (less than 0.2° warpage) isobtained.

Note that, the optical disk producing methods (1) and (2) given aboveare nothing but examples, and the method for producing an optical diskusing the optical disk producing sheet pertaining to this embodiment isnot limited to these two producing methods.

The embodiment described above was given for the sake of facilitating anunderstanding of the present invention, and not for the purpose oflimiting the present invention. Therefore, the elements disclosed in theabove embodiment also encompass all design modifications and equivalentsthat fall within the technical scope of the present invention.

For example, the release sheet 13 or the release sheet 13′ can beomitted in the optical disk producing sheet 1.

EXAMPLES

The present invention will now be described in more specific termsthrough examples and the like, but the scope of the present invention isnot limited to these examples and the like.

Example 1 1. Production of Coating Agent A for Stamper-Receiving Layer

80 parts by weight of n-butyl acrylate and 20 parts by weight of acrylicacid were reacted in a mixed solvent of ethyl acetate and methyl ethylketone (50:50 weight ratio). To the resulting acrylic ester copolymersolution (solids concentration: 35 wt %) was added2-methacryloyloxyethyl isocyanate in an amount of 30 equivalents per 100equivalents of acrylic acid in the copolymer. They were reacted for 48hours at 40° C. under a nitrogen atmosphere, which gave an energyrays-curable copolymer that had an energy rays-curable group on a sidechain thereof and had a weight average molecular weight of 850,000.

4.0 parts by weight ofoligo{2-hydroxy-2-methyl-1-[4-(1-propenyl)phenyl]propanone} which is aphotopolymerization initiator (Esacure KIP 150, made by Lamberti Spa),100 parts by weight of a composition composed of an energy rays-curablepolyfunctional monomer and oligomer (Seika Beam 14-29B (NPI), made byDainichiseika Colour & Chemicals), and 1.2 parts by weight of acrosslinking agent composed of a polyisocyanate compound (OribainBHS-8515, made by Toyo Ink) were dissolved per 100 parts by weight ofsolids of the energy rays-curable copolymer solution obtained above. Thesolids concentration was adjusted to 40 wt %, which gave a coating agentA for stamper-receiving layer.

2. Production of Coating Agent B for Adhesive Layer

75 parts by weight of n-butyl acrylate, 22 parts by weight of ethylacrylate, 3 parts by weight of acrylic acid, and 0.5 part by weight of2-hydroxyethyl acrylate were reacted in an ethyl acetate solvent toobtain an acrylic ester copolymer with a weight average molecular weightof 800,000.

0.06 part by weight of a metal chelate compound as a crosslinking agent(Alumichelate D made by Kawasaki Fine Chemical) was added per 100 partsby weight of solids of the acrylic ester copolymer obtained above, andthe solids concentration was adjusted to 25 wt %, which gave an coatingagent B for adhesive layer.

3. Production of Optical Disk Producing Sheet

Two types of release sheet were prepared: a heavy-release type ofrelease sheet (SP-PET3811, made by Lintec, surface roughness (Ra): 0.016μm) produced by release treatment of one side of a polyethyleneterephthalate (PET) film (thickness: 38 μm) with a heavy-release type ofsilicone resin, and a light-release type of release sheet (SP-PET3801,made by Lintec, surface roughness (Ra): 0.023 μm) produced by releasetreatment of one side of a PET film (thickness: 38 μm) with alight-release type of silicone resin.

The coating agent A was applied to the release-treated side of theheavy-release release sheet with a knife coater, and the coating wasdried for 1 minute at 90° C. to form a stamper-receiving layer with athickness of 10 μm. The release-treated side of the light-releaserelease sheet was applied to the surface of the stamper-receiving layer.Another light-release release sheet was then coated with the coatingagent B with a knife coater, and the coating was dried for 1 minute at90° C. to form an adhesive layer with a thickness of 15 μm. Thelight-release release sheet on the stamper-receiving layer was peeledaway, and the exposed stamper-receiving layer was faced the surface ofthe adhesive layer. The adhesive layer and the stamper-receiving layerwere laminated to obtain an optical disk producing sheet with a totalthickness of 25 μm.

Example 2 1. Production of Coating Agent C for Stamper-Receiving Layer

80 parts by weight of 2-ethylhexyl acrylate and 20 parts by weight of2-hydroxyethyl acrylate were reacted in an ethyl acetate solvent. To theresulting acrylic ester copolymer solution (solids concentration: 40 wt%) was added 2-methacryloyloxyethyl isocyanate in an amount of 78.5equivalents per 100 equivalents of 2-hydroxyethyl acrylate in thecopolymer, and 0.025 part by weight of dibutyltin dilaurate was added asa catalyst. They were reacted for 48 hours at 40° C. under a nitrogenatmosphere, which gave an energy rays-curable copolymer that had anenergy rays-curable group on a side chain thereof and had a weightaverage molecular weight of 800,000.

3.8 parts by weight of 1-hydroxycyclohexyl phenyl ketone as aphotopolymerization initiator (Irgacure 184, made by Ciba SpecialtyChemicals) was dissolved per 100 parts by weight of solids of the energyrays-curable copolymer solution obtained above, and the solidsconcentration was adjusted to 33 wt % to obtain a coating agent C forstamper-receiving layer.

2. Production of Coating Agent D for Stamper-Receiving Layer

91 parts by weight of n-butyl acrylate and 9 parts by weight of acrylicacid were reacted in an ethyl acetate solvent to obtain an acrylic estercopolymer with a weight average molecular weight of 600,000. 16.5 partsby weight of a polyisocyanate compound as a crosslinking agent (OribainBHS-8515, made by Toyo Ink) was added per 100 parts by weight of thesolids of the acrylic ester copolymer obtained above, and the solidsconcentration was adjusted to 30 wt % to obtain a coating agent D foradhesive layer.

3. Production of Optical Disk Producing Sheet

Other than using the above coating agent C for stamper-receiving layerand coating agent D for adhesive layer, an optical disk producing sheetwas produced in the same manner as in Example 1.

Example 3 1. Coating Agent for Stamper-Receiving Layer

The coating agent A for stamper-receiving layer produced in Example 1was used as the coating agent for stamper-receiving layer.

2. Production of Coating Agent E for Adhesive Layer

75 parts by weight of n-butyl acrylate, 10 parts by weight of ethylacrylate, and 3 parts by weight of acrylic acid were reacted in an ethylacetate solvent to obtain an acrylic ester copolymer with a weightaverage molecular weight of 900,000. 15 parts by weight of a compositioncomposed of an energy rays-curable polyfunctional monomer and oligomer(Seika Beam 14-29B (NPI), made by Dainichiseika Colour & Chemicals), 0.6part by weight of 1-hydroxycyclohexyl phenyl ketone as aphotopolymerization initiator (Irgacure 184, made by Ciba SpecialtyChemicals), and 3 parts by weight of polyisocyanate compound as acrosslinking agent (Oribain BHS-8515, made by Toyo Ink) were added to100 parts by weight of solids of the energy rays-curable copolymersolution obtained above. The solids concentration was adjusted to 30%,which gave a coating agent E for adhesive layer.

3. Production of Optical Disk Producing Sheet

Other than using the above coating agent E for stamper-receiving layer,an optical disk producing sheet was produced in the same manner as inExample 1.

Example 4 1. Coating Agent for Stamper-Receiving Layer

The coating agent A for stamper-receiving layer produced in Example 1was used as the stamper-receiving layer coating agent.

2. Coating Agent for Adhesive Layer

The coating agent E for adhesive layer produced in Example 3 was used asthe adhesive layer coating agent.

3. Production of Optical Disk Producing Sheet

The coating agent A was applied to the release-treated side of theheavy-release release sheet with a knife coater, and the coating wasdried for 1 minute at 90° C. to form a stamper-receiving layer with athickness of 10 μm. The release-treated side of the light-releaserelease sheet was applied to the surface of the stamper-receiving layer.Another light-release release sheet was then coated with the coatingagent E with a knife coater, and the coating was dried for 1 minute at90° C., after that the coating agent E was irradiated with UV rays(using an Adwill RAD-2000m/8 made by Lintec; irradiation conditions:luminance of 310 mW/cm², light quantity of 300 mJ/cm²) to form anadhesive layer with a thickness of 15 μm. The light-release releasesheet on the stamper-receiving layer was peeled away, and the exposedstamper-receiving layer was faced the surface of the adhesive layer. Theadhesive layer and the stamper-receiving layer were laminated to obtainan optical disk producing sheet with a total thickness of 25 μm.

Comparative Example 1

The coating agent A prepared in Example 1 was applied to therelease-treated side of the same heavy-release release sheet as inExample 1 with a knife coater, and the coating was dried for 1 minute at90° C. to form a stamper-receiving layer with a thickness of 25 μm. Thesame light-release release sheet as in Example 1 was laminated on thesurface of the stamper-receiving layer to obtain an optical diskproducing sheet.

Comparative Example 2

Other than changing the crosslinking agent in the coating agent Aprepared in Example 1 to N,N,N′,N′-tetraglycidylmetaxylenediamine(Tetrad-X, made by Mitsubishi Gas Chemical), an optical disk producingsheet was produced in the same manner as in Comparative Example 1.

Experiments 1. Measurement of Storage Elastic Modulus

The storage elastic modulus of the stamper-receiving layer prior tocuring and the storage elastic modulus of the adhesive layer, which wereformed in the examples and comparative examples, were measured at 1 Hzand 25° C. using a viscoelasticity measurement apparatus (DynamicAnalyzer RDA II, made by Rheometrics). The results are given in Table 1.

Also, the stamper-receiving layers formed in the examples andcomparative examples were irradiated with UV rays (using an AdwillRAD-2000m/8 made by Lintec; irradiation conditions: luminance of 310mW/cm², light quantity of 300 mJ/cm²) and the storage elastic modulus ofthe stamper-receiving layer after curing was measured at 3.5 Hz and 25°C. using a viscoelasticity measurement apparatus (Rheovibron DDV-II-EP,made by Orientec). The results are given in Table 1.

2. Production of Optical Disk

An optical disk substrate composed of polycarbonate and having aconcavo-convex pattern on one side (thickness: 1.1 mm, outside diameter:120 mm) was formed by injection molding, and a silver alloy reflectivelayer with a thickness of 80 nm was formed by sputtering over theconcavo-convex pattern. No concavo-convex pattern or silver alloyreflective layer was formed around the edge portion (1 mm width) of theoptical disk substrate.

The optical disk producing sheets produced in the examples andcomparative examples were punched out in the same shape as theabove-mentioned optical disk substrate, the light-release release sheetwas peeled off, and the exposed adhesive layer was laminated to theconcavo-convex pattern side of the optical disk substrate and pressbonded at a pressure of 29 N.

The heavy-release release sheet was then peeled off thestamper-receiving layer, and a transparent stamper made of norborneneresin was placed over the exposed stamper-receiving layer in a 25° C.atmosphere and press bonded at a pressure of 29 N, and theconcavo-convex pattern of the stamper was transferred onto thestamper-receiving layer.

Next, the stamper-receiving layer was irradiated with ultraviolet raysfrom the stamper side (using an Adwill RAD-2000m/8 made by Lintec;irradiation conditions: luminance of 310 mW/cm², light quantity of 300mJ/cm²) to cure the stamper-receiving layer and fix the concavo-convexpattern.

The stamper was separated from the stamper-receiving layer, after that atranslucent reflective layer composed of a silver alloy and having athickness of 10 nm was formed by sputtering on the surface of thestamper-receiving layer. A pressure sensitive adhesive layer (thickness:20 μm) which was formed separately using the coating agent B waslaminated on the translucent reflective layer, further a cover sheetcomposed of polycarbonate resin (Pure Ace C110-80, made by Teijin;thickness: 80 μm) was laminated on the pressure sensitive adhesivelayer. They were press bonded to obtain an optical disk.

After the being separated from the stamper-receiving layer, the stampersurface was examined at 200 power with a laser microscope (1LM21scanning laser microscope, made by Laser Tech), which revealed nodeposits on the surface of any of the stampers.

3. Measurement of Optical Disk Warpage

Each of the optical disks obtained above was placed in the mechanicalchuck of a disk inspection spindle motor (made by Chiba Precision;motor: DSBF50G-38M-249, driver: EDA-08C-012), the optical disk wasirradiated with a laser using a high-precision laser angle measurementdevice (made by Keyence; sensor head: LA-2010, controller: LA-2000), andthe angle of the reflected laser was measured. The warpage of theoptical disk was measured using the angle of the reflected laser as theangle of warpage of the optical disk. The results are given in Table 1.

4. Measurement of Adhesion to Polycarbonate (1) Production of Samplesfor Examples

The release-treated sides of release sheets were coated by knife coaterwith the coating agents for adhesive layer prepared in the examples,each coating was dried for 1 minute at 90° C. to form an adhesive layerwith a thickness of 15 μm, and a PET film with a thickness of 50 μm wasapplied to the surface thereof. When the adhesive layer coating agent ofExample 4 was used, an adhesive layer with a thickness of 15 μm wasformed by irradiating with UV rays (using an Adwill RAD-2000m/8 made byLintec; irradiation conditions: luminance of 310 mW/cm², light quantityof 300 mJ/cm²) after the coating of the adhesive layer coating agent hadbeen dried, and a PET film with a thickness of 50 μm was applied to thesurface of the adhesive layer.

Next, the release sheet was peeled off, and the exposed adhesive layerwas press bonded to a polycarbonate plate at a pressure of 20 N.

(2) Production of Samples for Comparative Examples

The light release sheet was peeled off each of the optical diskproducing sheets produced in the comparative examples, and a PET filmwith a thickness of 50 μm was applied with a laminator to the exposedstamper-receiving layer. The heavy release sheet was then peeled off,and the exposed adhesive layer was press bonded to a polycarbonate plateat a pressure of 20 N.

Each of the above samples was irradiated with UV rays from the PET filmside (using an Adwill RAD-2000m/8 made by Lintec; irradiationconditions: luminance of 310 mW/cm², light quantity of 300 mJ/cm²).After that, each sheet was peeled from the polycarbonate plate, and the180° peel strength at this time was measured. The results are given inTable 1.

TABLE 1 Adhesive Storage Disk strength to elastic modulus warpagepolycarbonate (Pa.25° C.) (deg.) (mN/25 mm) Example 1 stamper-receivingprior to curling 7.42 × 10⁴ −0.09 — layer after curling 1.62 × 10⁹adhesive layer 1.86 × 10⁵ 1750  Example 2 stamper-receiving prior tocurling 6.14 × 10⁴ −0.08 — layer after curling 3.20 × 10⁸ adhesive layer2.41 × 10⁵ 1500  Example 3 stamper-receiving prior to curling 7.42 × 10⁴−0.12 — layer after curling 1.62 × 10⁹ adhesive prior to curling 1.33 ×10⁵ 850 layer after curling 5.53 × 10⁶ Example 4 stamper-receiving priorto curling 7.42 × 10⁴ −0.10 — layer after curling 1.62 × 10⁹ adhesivelayer 5.53 × 10⁶ 700 Compar. stamper-receiving prior to curling 7.42 ×10⁴ −0.20  90 Example 1 layer after curling 1.62 × 10⁹ Compar.stamper-receiving prior to curling 7.40 × 10⁴ −0.24 145 Example 2 layerafter curling 1.16 × 10⁹

As is clear from Table 1, an optical disk obtained using one of theoptical disk producing sheets of the examples warps far less than anoptical disk obtained using one of the optical disk producing sheets ofthe comparative examples. Also, the optical disk producing sheets of theexamples have much higher adhesion strength to polycarbonate than theoptical disk producing sheets of the comparative examples.

INDUSTRIAL APPLICABILITY

With the optical disk producing sheet of the present invention,separation that occurs during the production of an optical disk, orduring the storage of the finished product, is prevented, and warpage inthe resulting optical disk is reduced. Namely, the optical diskproducing sheet of the present invention is useful in the production ofoptical disks because which can prevent or reduce warpage and interlayerseparation.

1. An optical disk producing sheet, comprising: a stamper-receiving layer that is energy rays-curable and has a storage elastic modulus prior to curing from 10³ to 10⁷ Pa; an adhesive layer directly laminated to the stamper-receiving layer, the adhesive layer having adhesive strength to polycarbonate of at least 200 mN/25 mm and a storage elastic modulus during the curing of the stamper-receiving layer of from 10³ to 10⁷ Pa; and a top release sheet and/or a bottom release sheet.
 2. The optical disk producing sheet according to claim 1, wherein the adhesive layer is a pressure sensitive adhesive.
 3. The optical disk producing sheet according to claim 2, wherein the pressure sensitive adhesive includes an acrylic ester copolymer.
 4. The optical disk producing sheet according to claim 1, wherein the stamper-receiving layer includes an acrylic ester copolymer having an energy rays-curable group on a side chain thereof.
 5. The optical disk producing sheet according to claim 1, wherein the stamper-receiving layer contains a carboxyl group-containing copolymer obtained by copolymerizing at least one type of monomer having a carboxyl group.
 6. An optical disk comprising a laminate obtained from an optical disk producing sheet, the laminate including: a stamper-receiving layer that is energy rays-curable and has a storage elastic modulus prior to curing from 10³ to 10⁷ Pa; and an adhesive layer directly laminated to the stamper-receiving layer, the adhesive layer having adhesive strength to polycarbonate of at least 200 mN/25 mm and a storage elastic modulus during the curing of the stamper-receiving layer of from 10³ to 10⁷ Pa.
 7. The optical disk producing sheet according to claim 6, wherein the adhesive layer is a pressure sensitive adhesive.
 8. The optical disk producing sheet according to claim 7, wherein the pressure sensitive adhesive includes an acrylic ester copolymer.
 9. The optical disk producing sheet according to claim 6, wherein the stamper-receiving layer includes an acrylic ester copolymer having an energy rays-curable group on a side chain thereof.
 10. The optical disk producing sheet according to claim 6, wherein the stamper-receiving layer contains a carboxyl group-containing copolymer obtained by copolymerizing at least one type of monomer having a carboxyl group. 